Process of producing viscose rayon



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United States Patent ica'n Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Filed Dec. 18, 1956, Ser; No. 628,997

Claims. (Cl. 18-54)' This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

The present application is a continuation in part of application Serial No. 466,671, filed November. 3, 1954, now abandoned.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a su'table cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanth ate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bod es such as filaments, the'viscose solution is extruded'through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dlute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell port'on anda core portion with a sharp line of demarkation between the two. The

cross section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts-are present in the spinning bath. The skin and core portions of the filament represent ditferences in structure and these different portions possess d'tferent swelling and staining characteristics, the latter permitting a-ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. .Although the core portion possesses a relatively h-gh tensile strength, it has alowabrasion resistance and a low flexlife, is subject to fibrillation and is relatively stiff.

It has-now been discovered that the presence ofsrnall amounts of alkali-soluble alkylene oxide adductsof'higher primary aliphatic-alcoholsinviscose results in the ,production of shaped bodies of regenerated cellulose asuch as filaments, films, sheets and the likecornposed of all and having improved-properties and characteristics providing that the amount of the adduct is maintained with ice 2 certain, lmitsandth'e composition of the spinning bath, is maintained within certain composition limits which will be defined hereinafter. T hemost readily distinguishable characteristics. as compared to conventional filaments include a smooth, nonrcrenulated. surface andvthe; filaments consist substantially entirely of skin.-

This invention contemplates, the use of such compounds as are-moretechnically classed as polyoxyalkylene glycolv ethers of higher primary aliphatic, or fatty alcohols such as, for example, the ethers of ethylene and propylene glycols and the alcohols. Itis, obvious that for all, practical purposes considering cost, ease of preparation, commercial availability andj solubility in water and alkali solutions such. as. a. 6 percent caustic, solution, the polyoxyethylene. oxide compounds are preferred, Accordingly, the invention will be illustrated-by reference to polyoxyethylene glycol ethers. As is well known, the substances as. commercially prepared generally are not pure compounds but consist of a group of ethers.

The higher pr'mary aliphatic alcohols contemplated for use in the ethers contain from 8 to 24 carbon atoms, preferably from 12 to 18 carbon atoms. The ethers may be prepared from a relatively pure alcohol withinthe range or they may be prepared from technical grades of the alcohols or a mixture of the alcohols as derive rom the acid radicals of naturally occurring fats and oils such as cottonseed oil, coconut oil, corn oil, soya. beanoil, palm oils, peanut oil and the like and, the hydrogenated fats and o'ls, the hydrocarbon chains being of the same number of carbon atoms as the fatty acids in which they have their origin. The alcohols derivedfrom coconut oil, for example, will consist of a. mixture of alcohols having from 8 to 18. carbon atoms with the individual alcohols in a distribution corresponding to, the'percentage distribution of the fatty acids of the particular coconut oil.

The polyoxyalkylene or polyoxyethylene content of the adducts or ethers may vary from about 20 to 200 nd more alkylene oxide units per molecule of aliphatic alcohol, the preferred ethers containing from about 30 to about.150 ethylene oxide units per molecule, The ethers may be uniform in respect to the ethylene ox-de chain or the substance may consist of a mixture of ethers having ethylene oxide chains of different length depending upon the method of preparation of the ethers, It is to: he understood that for the purposes of this invention each of the chains of ethylene oxide units need not be identical.

The production of all skTn products requires that, certain minimum amounts of the ether be in solution in the viscose. Therefore, the minimum number of units of an alkylene oxide such as ethylene oxide required in the I.

ether is that amount which imparts to the aliphatic alcohol ether suificfent alkali solubility wherebythe minimum amount of ether can be dissolved in the viscose;

The ether may be conveniently added to the viscose inithe form of a solution in alkali or water. It is preferred .to

the production of the viscose. V i

The amount of the polyoxyalkylene glycolaliphatic alcohol ether which is incorporated in viscose nust t least about 1 percent by weight of the cellulose lll tll 'theamount varies from 2 percent to 5 percent. Lesser amounts do not result in the productionof produgtsconsisting entirely of skin and greater amountsafter: versely the physical properties of the products. m

within the preferredrange are most effective in .enlia 5-" ing the characteristics and properties qf tl1 e.,proglucts. The polyoxyalkylene glycol-alcohol ether may be added viscose and may vary up to about 6 percent, preferably,

at any one of the stages in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The polyoxyalkylene glycol-aliphatic alcohol ether is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 4 percent to about percent cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4 percent to about 11 percent and the carbon disulfide content may be from about 35 percent to about 60 percent based upon the weight of the cellulose. The modified viscose, that is, a viscose containing a small amount of the ether adduct, should have a salt test number or index of at least 7 and preferably about 8.0 or higher at the time of spinning or extrusion. The salt test is an indication of both the amount of carbondisulfide added to the viscose and the degree of aging. The salt test number is the minimum percent concentration of sodium chloride solution at 18 C. required to coagulate 3 drops of viscose. It is determined by dropping the viscose into a beaker containing about 40 cc. of sodium chloride solution at 18 C. while stirring. Stirring is continued for 90 seconds after the last drop of viscose has been added.

In order to obtain the improvements heretofore mentioned, and particularly to obtain all skin, or substantially all-skin yarn with its resulting advantages, it has been found that in addition to the presence of the additives of the present invention, the amount of carbon disulfide used in the preparation of the viscose and the acid and zinc contents of the acid spinning bath are important. The presence of the modifier of this invention in a viscose of required carbon disulfide content combined with these spinning baths results in the production of yarns of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consisting of filaments composed substantially or entirely of skin.

In practicing the present invention the carbon disulfide added in preparing the viscose should be at least 35 percent, based on the bone dry cellulose content, and preferably in the order of 38 percent to 50 percent.

Also, generically and in terms of the industrial art, the spinning bath used in the practice of the present invention is a low acid-high zinc spinning bath. The bath should contain from about 10 percent to about 25 percent sodium sulfate and from about 4 percent to about percent zinc sulfate, preferably from 15 percent to 22 percent sodium sulfate and from 5 to 12 percent zinc sulfate. Other metal sulfates such as iron, manganese,

nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 C., though at the lower temperatures the higher concentrations of sodium sulfate cannot be used because of the difiiculty of solubility. However, at the preferred temperatures of between about 40 C. to about 70 C. solubility is no problem. In the production of the all-skin type filaments, the temperature of the spinning bath is not critical. However, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength are affected by the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 40 C. and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced 'against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. Though for any given spinning conditions a substantially higher percentage of skin will be obtained through the use of the additives of the present invention, in order to get an allskin yarn the carbon disulfide content of the viscose should preferably be at least 38 percent based on the dry cellulose. Also, the acid content of the spinning bath should preferably generally not exceed about 8.0 percent while the zinc sulfate is preferably maintained within the range of 5 percent to 12 percent. However, frequently in commercial spinning practice, it is desirable to have a somewhat higher acid content in the spinning bath. It has been found that higher acid contents can be used for any given amount of additive and still exceptionally high-skin and all-skin yarns obtained if the carbon disulfide content of the viscose is increased and the zinc sulfate content of the bath maintained at a reasonable high level such as above 8.0 percent. Thus, even though in practicing the present invention for the production of all-skin products, it is generally preferred that the acid concentration of the bath not exceed about 8 percent all-skin products will be obtained at higher acid concentrations up to as high as 10 percent if the carbon disulfide content of the viscose is sufficiently increased and the zinc sulfate of the spinning bath is not appreciably below 8.0 percent. Of course, increasing the amount of additive, within the range specified, also permits, to some degree, the use of higher acid concentrations in the spinning bath. As a general rule it can be stated, in practicing the present invention with the additives mentioned, that if difficulty is encountered in obtaining a percent skin product because of the desire to use a spinning bath having an acid content in excess of 8 percent somewhat higher acid concentrations can be used by using a viscose of higher carbon disulfide content and by increasing the zinc sulfate content of the bath within the limits indicated.

Though various terminology may be used to indicate the point at which the viscose is sufficiently coagulated to permit uniform withdrawal from the spinneret, for purposes of the present application the term slubbing point will be used. This lower acid concentration is readily determined by those skilled in the art through observance of the fibers as formed and has no particular effect on the production of high-skin or all-skin products in practicing the present invention. In general, the lower limit of sulfuric acid required in order to give sufiicient coagulation for spinning, for example with a viscose containing 7 percent cellulose and 6 percent caustic, is about 6 percent. Another way of stating this is that an acid concentration of about 6 percent is slightly above the slubbing point. It is apparent that for viscose with higher caustic content a slightly higher acid concentration would be required due to the partial neutralizing effect of the increased caustic.

It is clear from the above that there is a maximum acid concentration for any specific viscose composition of given carbon disulfide content beyond which substantially all-skin products will not be obtained with the present additives. It is also clear that this maximum acid concentration can be somewhat increased through the use of higher concentrations of zinc sulfate in the spinning bath and by increasing the carbon disulfide content of the viscose. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of all and substantially all-skin products from a 7 percent cellulose, 6 percent caustic, 38 percent carbon disulfide (based on the weight of the cellulose) viscose containing the above mentioned polyoxyalkylene glycolaliphatic alcohol ethers, lies between about 6 percent and about 8 percent. The acid concentration may be increased as ,the amount of additive is increased and also {StlfQtChQd as low as 20 percent.

as the salt test of theviscose isincreased. There isan upper limit, however, for the acid concentration based upon the amount of modifier and the concentration of caustic in the viscose. Allaskin products cannotbe obtained if the acid contentof the ,bathis increased above the maximum value even though the amount of added modifier is increased to as ,much'asufipercent while other conditions are maintained constant. For example, avis cose containing about 7 percent cellulose, ab Q u t- 6;.percent caustic soda, and, basedgon the weightof the cellulose, about 41 percentqcarbonudisulfide and 3 percent of a polyoxyethylene glycol ether of deeanol having about 30 ethylene oxide unitspermoleeule and the viscose having a salt test of 9 to '10 whemextruded iintotspinning baths containing 16 percentito ,20;.percent:sodium sulfate, 4 percent to 8 percent zinc sulfate :and sulfuric acid of not more than about 8 PGICfiIlLIQSHltS in the:pr.oduc tion of all-skin filaments. Lesser amountsyofsulfuric acidmay be employed. Greateramounts of acid-,resultin the .production of products having {skin andcore. At .acid concentrations in excess of-8 percent theskin would generally comprise less than 85 percent of the filament. By increasing the carbon disulfide content to 45 percent, however, and increasing the zinc sulfate content of the acid spinning bath to about 10 percent the acid concentration of the spinning bath can be increased to asmuch as 10 percent and similar results can be obtained.

It has been determined that the maximum permissible acid content of the bath is approximately 0.2 times the carbon disulfide of the viscose as based on the dry cellulose and is preferably about 0.18 to-0..l9 times the carbon disulfide content of the viscose. It is also generally preferred that the acid content of'thespinning hath not exceed about 1.35 times .the caustic soda content ofthe viscose.

The presence of the polyoxyalkylene glycol-aliphatic alchol ethers in the viscose retards the coagulation and,

therefore, the amount of the ether employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all-skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, the ether is employed in amounts within the lower portion of the range, for example, about 1.0 percent to 1.5 percent. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinningrspeed is a matter of simple experimentationfor those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath :for. a period sufficient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufficient so that the filaments will not adhere to each other as they are brought together and Withdrawn from the bath.

In the production of filaments .for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water L01 a dilute acid solution and may be stretched from about 70 percent to about 110 percent, preferably between 85 :percent and 100 percent. Yarns for other textile purposes may be The precise amount of stretching will be dependentrupon the desired tenacity and other properties andthe .specifictype of product being produced. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable toother shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 11 percent :to about 5 percent sulfuricacid and from about l percent-to about 5 percent sodium sulfate with or without small amounts of 'zinc sulfate if regeneration has not previously been completed.

The treatment followingthefinal regenerating bath,

.or the stretching'operation where regenerationzhas been completed, may consistof a washing'step,;a desulfurizing .step, the applicationof afinisliing or :plasticizing material and drying before or after collecting, or mayinclude other desired and conventionalsteps such as bleaching and the like. The treatment after regeneration ,will be dictated by the specific type of shapedibody and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of the alkali-soluble polyoxyalkylene glycol ethers of the primary alcohols and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the jfilament, the swelling and staining characteristics are uniform throughout the cross section of the filament. Filamentsproduced pursuant .to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to .prior methods which may be attributed by the uniformity in skin structure through the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss oftensile strength, there is appreciably less loss in tensile strengthin the production of twisted cords from the filamentsconsisting entirely or skin. Filaments prepared from viscose containing the polyoxyalkylene glycol ethers of the primary alcohols have 'a high tensile strength astcompared to normal regenerated cellulose filaments, have superior abrasion and fatigue resistance 'characteristics'and have a high flex-life. Such filaments are highly satisfactory for the production of cords -for'the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted tosuch uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a-viscose containing about 7 percent cellulose, about 6 percent caustic soda, and having a total carbon disulfide content of about 41 percent based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36 percent carbon disulfide, based on the weight of the cellulose and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. An additional 5 percent carbon disulfide was then added'to the mixer and the mass mixed for about one hour. The polyoxyethylene glycol-aliphatic alcohol ether was added to the caustic soda solution. and mixed for about /2 hour. The viscose was then allowed to ripen for about 30 hours at 18 C.

Example I Approximately 2 percent (based on the weight of the cellulose) of a polyoxyethylene glycol ether of technical grade, stearyl alcohol having about ethylene oxide units per mole of the alcohol was added to and incorporated in the viscose as described above. The viscose employed in the spinning of filaments had a salt test of 9.4. The viscose was extruded through a spinneret at a rate of about 22 meters per minute to form a 1650 denier,

720 filament yarn for the production of a tire cord. The

coagulating and regenerating bath was maintained'at a temperature of about 60 C. and contained 7percent sulfuric acid, 8 percent zinc sulfate and 17 percent sodium sulfate. The yarn was passed over a godet from which it was conducted to threadaadvancing reels where it was stretched about 100 percent, Washed freeof acid and salts, dried and collected on cones.

The individual filaments have a smooth, non-crenulated exterior surface and consist entirely ofskin, no core being detectable at high magnification (e.g. 11500 The filaments of a control yarn spun with ithejsame viscose but without the addition of the polyoxyethylene {glycolaliphatic alcohol ether and spun under the same condis core with a sharp line of demarkation between the skin and core.

Example II Example I was repeated by spinning a viscose solution as described under the same conditions except that the filaments were stretched approximately 85 percent while passing between the thread advancing reels.

The individual filaments were readily distinguishable from control filaments prepared from viscose containing no modifier in that they have a smooth, non-crenulated surface and consist entirely of skin. Control filaments have a very irregular and serrated surface and consist of about 70 percent skin and the balance core with a sharp line of demarkation between the skin and core. The tenacity and elongation of the filaments of this example are slightly lower than that of the filaments of Example I.

Example III To a viscose solution as described above, there was added 3 percent of a polyoxyethylene glycol ether of decanol having about 30 ethylene oxide units per molecule. The viscose had a salt test of 8.5 and was spun into a 200 denier, 120 filament yarn by extrusion into a bath containing 7.5 percent sulfuric acid, 8 percent zinc sulfate and 19 percent sodium sulfate. The bath was maintained at a temperature of 60 C. The extrusion rate was about 22 meters per minute. The water bath was maintained at a temperature of 95 C. and the filaments were stretched 82 percent while passing through the hot water. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The individual filaments had a smooth, non-crenulated surface and consist entirely of skin while control filaments have a very irregular and serrated surface and consist of 70 percent skin and the balance core with a sharp line of demarkation between the skin and the core.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65 percent to about 80 percent for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45 percent to about 60 percent.

If desired, small amounts of the polyoxyalkylene glycol-aliphatic alcohol ether may be added to the spinning bath. Since the substances are also water-soluble, some of the modifier will be leached from the filament and will be present in the bath.

The modifier of this invention may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The polyoxyethylene glycol-aliphatic alcohol ether may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material provided that the amount present will produce a viscose having the proper proportion of the ether at the time of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome .section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60 percent and 30 percent alcohol for a few moments each, and it is then stained in 2 percent aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled Water and then in one or more baths composed of percent water. and 90 percent dioxane for a 8 period of varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim: 1. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin,

cent caustic soda, from about 35 percent to 60 percent carbon disulfide based on the weight of the cellulose and I from about 1 percent to about 6 percent of a substance selected from the group consisting of alkali-soluble polyoxyalkylene glycol ethers of higher primary aliphatic alcohols and mixtures thereof, based on the weight of the cellulose in the viscose, into an aqueous spinning bath containing from about 10 percent to 25 percent sodium sulfate, from about 4 percent to 15 percent zinc sulfate and sulfuric acid, the percent sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 0.2 times the percent carbon disulfide content of said viscose.

2. The steps in the method as defined in claim 1 wherein the shaped bodies consist of filaments and the polyoxyalkylene glycol ethers are polyoxyethylene glycol ethers having from about 30 to ethylene oxide units per molecule.

3. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the steps which include extruding a viscose having a salt index of at least 8 and containing from about 4 percent to 10 percent cellulose, from about 4 percent to 11 percent caustic soda, from about 38 percent to 50 percent carbon disulfide based on the weight of the cellulose and from about 2 percent to about 5 percent, based on the weight of the cellulose in the viscose, of a substance from the group consisting of alkali-soluble polyoxyalkylene glycol ethers of higher primary aliphatic alcohols and mixtures thereof into an aqueous spinning bath containing from about 10 percent to 25 percent sodium sulfate, from about 5 percent to 12 percent zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8 percent, removing the body from the spinning bath, washing the body and drying the body.

4. The steps in the method as defined in claim 3 wherein the shaped bodies consist of filaments and the polyoxyalkylene glycol ethers of polyoxyethylene glycol ethers having from about 30 to 150 ethylene oxide units per molecule.

5. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in a viscose from about 1 percent to about 6 percent of a substance selected from the group consisting of alkali-soluble poly oxyalkylene glycol ethers of higher primary aliphatic alcohols and mixtures thereof, based on the weight of the cellulose in the viscose, the viscose containing from about 4 percent to 10 percent cellulose, from about 4 percent to 11 percent caustic soda and from about 38 percent to 50 percent carbon disulfide based upon the weight of the cellulose, and extruding the viscose at a salt index of at least 8 into an aqueous spinning bath containing from about 10 percent to 25 percent sodium sulfate, from about 4 percent to 15 percent zinc sulfate and sulfuric acid, the percentage sulfuric acid content of the bath exceeding the slubbing point but not exceeding about 0.19 times the percentage carbon disulfide content of the viscose.

6. The method as defined in claim 5 wherein the polyoxyalkylene glycol ethers are polyoxyethylene glycol ethers having from about 30 to 150 ethylene oxide units per molecule.

7. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in a viscose from 2 percent to 5 percent of a substance selected from the group consisting of alkali-soluble polyoxyalkylene glycol ethers of higher primary aliphatic alcohols and mixtures thereof, based on the weight of the cellulose in the viscose, the viscose containing about 7 percent cellulose, about 6 percent caustic soda and about 41 percent carbon disulfide based upon the weight of the cellulose, ripening the viscose to a salt point of not less than 8 and extruding the viscose into an aqueous spinning bath containing from about 15 percent to 22 percent sodium sulfate, from about 5 percent to 12 percent zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8 percent.

References Cited in the file of this patent UNITED STATES PATENTS 2,519,227 Collins Aug. 15, 1950 2,535,044 Cox Dec. 26, 1950 2,664,360 Charles et a1 Dec. 29, 1953 2,710,861 Charles et al June 14, 1955 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISTING SUBSTANTIALLY ENTIRELY OF SKIN, THE STEPS WHICH INCLUDE EXTRUDING A VISCOSE HAVING A SALT INDEX OF AT LEAST 7 AND CONTAINING FROM ABOUT 4 PERCENT TO 10 PERCENT CELLULOSE, FROM ABOUT 4 PERCENT TO 11 PERCENT CAUSTIC SODA, FROM ABOUT 35 PERCENT TO 60 PERCENT CARBON DISULFIDE BASED ON THE WEIGHT OF THE CELLULOSE AND FROM ABOUT 1 PERCENT TO ABOUT 6 PERCENT OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF ALKALI-SOLUBLE POLYOXYALKYLENE GLYCOL ETHERS OF HIGHER PRIMARY ALIPHATIC ALCOHOLS AND MIXTURES THEREOF, BASED ON THE WEIGHT OF THE CELLULOSE IN THE VISCOSE, INTO AN AQUEOUS SPINNING BATH CONTAINING FROM ABOUT 10 PERCENT TO 25 PERCENT SODIUM SULFATE, FROM ABOUT 4 PERCENT TO 15 PERCENT ZINC SULFATE AND SULFURIC ACID, THE PERCENT SULFURIC ACID CONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT NOT EXCEEDING ABOUT 0.2 TIMES THE PERCENT CARBON DISULFIDE CONTENT OF SAID VISCOSE. 